The present invention relates to organic light emitting diode (OLED) displays, and more particularly, to improving the performance, reliability, and robustness of such displays by preventing moisture from degrading the light-emitting OLED materials and improving the contrast of the display.
Organic light-emitting diode (OLED) display devices require humidity levels below about 1000 parts per million (ppm) to prevent premature degradation of device performance within a specified operating and/or storage life of the device. Control of the environment to this range of humidity levels within a packaged device is typically achieved by encapsulating the device or by sealing the device and a desiccant within a cover. Desiccants such as, for example, metal oxides, alkaline earth metal oxides, sulfates, metal halides, and perchlorates are used to maintain the humidity level below the above level. See for example U.S. Pat. No. 6,226,890 B1 issued May 8, 2001 to Boroson et al. describing desiccant materials for moisture-sensitive electronic devices. The device disclosed in FIG. 2 of Boroson et al. is a so-called bottom emitting OLED device that emits light through a transparent substrate. The desiccant material is located over the organic light emitting materials in an enclosure that is sealed to the back-side of the substrate.
In a so-called top emitting OLED the organic material is also located on a substrate, but the light is emitted from the surface of the substrate through a transparent cover plate that also serves as part of the sealed enclosure. In this arrangement, desiccant materials located in the enclosure over to the organic materials will interfere with the light emitted by the OLED.
There is a need therefore for an improved means to provide desiccation in a top-emitting OLED display device.
The need is met by providing a top-emitting OLED display device, that includes a substrate; an array of OLED elements disposed on one side of the substrate; and a desiccant material provided in a patterned arrangement over the array of OLED elements on the same side of the substrate such that the desiccant material does not interfere with the light emitted by the OLED elements.
According to a preferred embodiment of the invention, the patterned arrangement of desiccant material performs the function of a black matrix for increasing the contrast of the display.
The present invention has the advantage that it increases the lifetime of a top-emitting OLED display device by providing desiccation of the OLED elements. In a preferred embodiment, the contrast of the display is also improved.